# [R] selectively altering variable value

jim holtman jholtman at gmail.com
Mon Aug 3 18:04:39 CEST 2009

```This should set the first two ia==4 entries to 1 in saccade column:

> x
1   1     1  5       0
2   1     1  5       0
3   1     1  5       0
4   1     1  5       1
5   1     1  5       1
6   1     1  9       1
7   1     1  9       1
8   1     1  9       1
9   1     1  4       1
10  1     1  4       0
11  1     2  5       0
12  1     2  5       0
13  1     2  5       0
14  1     2  5       1
15  1     2  5       1
16  1     2  9       1
17  1     2  9       1
18  1     2  9       1
19  1     2  4       1
20  1     2  4       1
21  1     2  4       0
22  1     2  4       0
23  1     3  5       0
24  1     3  5       0
25  1     3  5       0
26  1     3  5       1
27  1     3  5       1
28  1     3  9       1
29  1     3  9       1
30  1     3  9       1
31  1     3  4       0
32  1     3  4       0
33  1     3  4       0
34  1     4  5       0
35  1     4  5       0
36  1     4  5       0
37  1     4  5       1
38  1     4  5       1
39  1     4  9       1
40  1     4  9       1
41  1     4  9       1
42  1     4  4       0
43  1     4  4       0
44  1     4  4       0
45  1     4  4       0
46  1     4  4       0
47  1     4  4       0
> # find the runs of 'ia'
> z.rle <- rle(x\$ia)
> # get the offsets of each sequence
> z.rle\$offset <- cumsum(c(1,z.rle\$lengths))
> ia4 <- which(z.rle\$values == 4)
> for (i in ia4){
+     # set all the saccade values to 0
+     # set at most the first two to 1
+     x\$saccade[seq(z.rle\$offset[i], length=min(2, z.rle\$lengths[i]))] <- 1
+ }
>
> x
1   1     1  5       0
2   1     1  5       0
3   1     1  5       0
4   1     1  5       1
5   1     1  5       1
6   1     1  9       1
7   1     1  9       1
8   1     1  9       1
9   1     1  4       1
10  1     1  4       1
11  1     2  5       0
12  1     2  5       0
13  1     2  5       0
14  1     2  5       1
15  1     2  5       1
16  1     2  9       1
17  1     2  9       1
18  1     2  9       1
19  1     2  4       1
20  1     2  4       1
21  1     2  4       0
22  1     2  4       0
23  1     3  5       0
24  1     3  5       0
25  1     3  5       0
26  1     3  5       1
27  1     3  5       1
28  1     3  9       1
29  1     3  9       1
30  1     3  9       1
31  1     3  4       1
32  1     3  4       1
33  1     3  4       0
34  1     4  5       0
35  1     4  5       0
36  1     4  5       0
37  1     4  5       1
38  1     4  5       1
39  1     4  9       1
40  1     4  9       1
41  1     4  9       1
42  1     4  4       1
43  1     4  4       1
44  1     4  4       0
45  1     4  4       0
46  1     4  4       0
47  1     4  4       0
>

On Mon, Aug 3, 2009 at 11:05 AM, Jens Bölte<boelte at psy.uni-muenster.de> wrote:
> Hello,
>
> I have run an eye-tracking experiment for which I now like to analyse the
> saccades. Participants looked from a fixation cross (ia = 5) to the target
> area (ia = 4) in following example of a data frame. ia = 9 stands for
> everything else. A saccade is indicated by saccade = 1. Sometimes the
> saccade just ends before the target area (see below). This is due to the
> parameters that determine a saccade and a fixation and some measurement
> error (accuracy of the eyetracker). I like to include the first two
> no-saccades in a target area into the saccade. The simplest approach, at
> least to my knowledge, would be to replace the value saccade = 0 with
> saccade = 1 for the first two ia = 4 (see the example below). But that is
> beyond my rather limited knowledge in R.
> My data frame is structured as follows (.... stands for multiple rows; just
> deleted for presentation purposes)
>
> vp trial ia saccade (other columns deleted for presentation purposes)
> 1 1 5 0
> 1 1 5 0
> 1 1 5 0
> 1 1 5 1
> 1 1 5 1
> ....
> 1 1 9 1
> 1 1 9 1
> 1 1 9 1
> ....
> 1 1 4 1
> 1 1 4 0
> .....
> 1 2 5 0
> 1 2 5 0
> 1 2 5 0
> 1 2 5 1
> 1 2 5 1
> ....
> 1 2 9 1
> 1 2 9 1
> 1 2 9 1
> ....
> 1 2 4 1
> 1 2 4 1
> 1 2 4 0
> 1 2 4 0
>
> aso. more trials follow (up 72).
> 1 3 5 0
> 1 3 5 0
> 1 3 5 0
> 1 3 5 1
> 1 3 5 1
> ....
> 1 3 9 1
> 1 3 9 1
> 1 3 9 1
> ....
> 1 3 4 0 <- how do I get  -> 1 3 4 1
> 1 3 4 0 <- how do I get  -> 1 3 4 1
> 1 3 4 0 <- how do I keep -> 1 3 4 0
> .....
> 1 4 5 0
> 1 4 5 0
> 1 4 5 0
> 1 4 5 1
> 1 4 5 1
> ....
> 1 4 9 1
> 1 4 9 1
> 1 4 9 1
> ....
> 1 4 4 0 <- how do I get  -> 1 4 4 1
> 1 4 4 0 <- how do I get  -> 1 4 4 1    1 4 4 0 <- how do I keep -> 1 4 4 0
> 1 4 4 0 <- how do I keep -> 1 4 4 0
> 1 4 4 0
> 1 4 4 0
> 1 4 4 0
>
> Thanks a lot for any help
>
> Jens
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.
>
>

--
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

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